The optical fiber distributed sensing technology allows for continuous measurement on external physical parameters distributed along a geometric path of optical fiber, and is widely used in the fields of intelligent bridge, expressway, important building and gas pipeline monitoring, etc. With regard to optical fiber distributed monitoring, there are mainly two kinds of distributed monitoring systems, i.e., intensity demodulation-based distributed monitoring systems and phase demodulation-based distributed monitoring systems, wherein the intensity demodulation distributed monitoring systems can only demodulate the light intensity variation information of the Rayleigh backscattering light in a unit pulse and has a limited application scope, while the phase demodulation distributed monitoring systems can demodulate the phase information of the interference light of the Rayleigh backscattering light in a unit pulse and has a wide range of application scenarios. At present, the phase demodulation solutions of a phase demodulation distributed monitoring system mainly consist of two solutions, i.e., phase generated carrier (PGC) and 3×3 coupler demodulation.
The PGC solution requires the addition of carrier and requires signal acquisition for the interference light and the modulation waves simultaneously, that is, it needs to demodulate two signals at the same time, so both the frequency and the amplitude of the carrier need to be quantized strictly to meet the requirement of the system demodulation accuracy, in addition, the dynamic range of the system is limited by the carrier frequency. The 3×3 coupler demodulation requires simultaneous signal acquisition of three signals, which involves larger data amount and makes the system complicated. The principle of the 3×3 coupler demodulation is based on an angle of 120°, but the 3×3 coupler actually produced do not precisely have the 120°, thus, the angle of the 3×3 coupler also affects the demodulation accuracy.
To sum up, the process of acquiring demodulation data in the prior art is relatively complicated, and there are many factors affecting accuracy, resulting in low accuracy of the acquired demodulation data.